1. Field of the Invention
The present invention relates to a system for driving a semiconductor laser, and more particulary to a semiconductor laser driver system capable of preventing mode hopping noise of a semiconductor laser driven thereby.
2. Description of the Prior Art
There are known optical scanning devices for scanning a recording medium with a light beam to record various information such as image information on the recording medium and to read out various information recorded on the recording medium. The light beam used in those optical scanning devices is typically a laser beam emitted from a semiconductor laser.
Where an image having a continuous gradation is to be recorded or read out by scanning the same with a laser beam, the quantity of the emitted laser beam is not allowed to fluctuate by more than a maximum level of about 0.2%.
Semiconductor lasers are susceptible to mode hopping noise under certain conditions in which they are driven. More specifically, the semiconductor laser produces light emission in different modes (wavelengths) under certain conditions. The laser output beam emitted from the semiconductor laser mode hops, i.e., it is shifted from one mode to another and back. Repeated mode hopping causes the quantity of the laser beam to fluctuate, generating mode hopping noise. The quantity of fluctuation of the emitted laser beam due to the mode hopping noise sometimes reaches a few % of the overall laser output power. Therefore, if a laser beam for recording or reading out continuously gradational image formation should suffer from mode hopping noise which causes a few % of laser beam fluctuation, then the recorded or read-out image information would contain irregularities in its gradations.
Consequently, semiconductor lasers used for scanning recording mediums for recording and reading out image information or the like are required to be driven in a manner to avoid the generation of mode hopping noise. However, conventional semiconductor laser drivers are not designed to sufficiently suppress mode hopping noise.